These confidence intervals (CI) are ranges of values that are likely to contain the true value of the coefficient for each term in the model.
Because samples are random, two samples from a population are unlikely to yield identical confidence intervals. However, if you take many random samples, a certain percentage of the resulting confidence intervals contain the unknown population parameter. The percentage of these confidence intervals that contain the parameter is the confidence level of the interval.
The confidence interval is composed of the following two parts:
- Point estimate
- This single value estimates a population parameter by using your sample data. The confidence interval is centered around the point estimate.
- Margin of error
- The margin of error defines the width of the confidence interval and is determined by the observed variability in the sample, the sample size, and the confidence level. To calculate the upper limit of the confidence interval, the margin of error is added to the point estimate. To calculate the lower limit of the confidence interval, the margin of error is subtracted from the point estimate.
You often use orthogonal regression in clinical chemistry or a laboratory to determine whether two instruments or methods provide comparable measurements. If the confidence interval for the constant term contains zero and the interval for the linear term contains 1, then you can usually conclude that the measurements from the two instruments are comparable.
In these results, the confidence interval for the constant term is approximately (−3, 4). Because the interval contains 0, this part of the analysis does not provide evidence that the measurements from the two instruments differ.
The confidence interval for the linear term is approximately (0.97, 1.02). Because the interval contains 1, this part of the analysis does not provide evidence that the measurements from the two instruments differ.
Orthogonal Regression Analysis: New versus Current
Error Variance Ratio (New/Current): 0.9
New = 0.644 + 0.995 Current
Predictor Coef SE Coef Z P Approx 95% CI
Constant 0.64441 1.74470 0.3694 0.712 (-2.77513, 4.06395)
Current 0.99542 0.01415 70.3461 0.000 ( 0.96769, 1.02315)